The Cell Biology & Microinjection Service provides researchers with valuable tools for studies of gene expression in vivo and a mechanism for creating induced mutations. The Service provides the expertise and supplies necessary for embryonic stem cell (ES cell) culture and manipulation, ES cell aggregation, and both blastocyst and pronuclear injection for the creation of targeted mutant and transgenic mice, which can be produced on both inbred and hybrid genetic backgrounds. C57BL/6J, 129/ImJ and a host of hybrid 129 ES cell lines have been derived and tested by the Service?s staff, and are available for use. In addition, the highly skilled technical staff perform technically challenging protocols such as pronuclear injection of very large (>200kb) BAC clones. Service is provided to Cancer Center staff at the level required; investigators can forward manipulated ES cells to the Service for microinjection and chimera production, or they may opt to forward DNA constructs for electroporation, ES cell cloning, screening, and microinjection. Related services and reagents are available including pathogen-free timed pregnancies, superovulated and vasectomized mice, premeasured and tested hormones, feeder cells, and cell culture supplies. The Service assists in the breeding of founder and chimeric mice, complete ovarian transplants, and timed harvesting of eggs. Cell Biology & Microinjection has been supported by Cancer Center support grant (CCSG) funds for the past five years, during which time use of the Service has increased an average of 33.7 percent. Thomas Gridley, Ph.D., a developmental biologist, has served as the Scientific Staff Supervisor since 1999. Dr. Gridley communicates regularly with the User Group and service personnel to insure that users have equitable service access and that their needs are met in the most efficient, cost effective and technically current manner. Service's staff work closely with Microchemistry Service staff to provide comprehensive tools and capabilities to Cancer Center staff for state-of-the-art genetic engineering.